1. Field of the Invention
The present invention relates to aqueous emulsions containing polyvinyl butyral and processes for their preparation and methods of their use.
2. Description of Related Art
Aqueous emulsions which include polyvinyl butyral are known. The emulsifiers they contain are in most cases anionic compounds such as salts of fatty acids, alkanesulfonates or alkyllaurylsulfonates. See U.S. Pat. Nos. 2,686,724, 2,532,223, 2,611,755, and 2,509,667.
However, emulsions of this kind, i.e., containing ionic emulsifiers, are sensitive to changes in pH, and therefore are not suitable for every application. Emulsions containing nonionic emulsifiers, on the other hand, are stable to pH change.
JP-A 58/026374 describes aqueous emulsions of polyvinyl butyral which are free of anionic emulsifiers. These emulsions contain not only the polyvinyl butyral but also polyvinyl alcohol, a so-called plasticizer resin, in order to improve the film-forming properties and the elasticity. The emulsions also must contain a so-called petroleum resin to achieve sufficient stability of the dispersion. These emulsions have to be prepared under pressure.